Focal negative motor seizures: Multimodal evaluation

Abstract

This case report shows the importance of multimodal evaluation to formulate a proper diagnosis of negative motor seizures (NMSs). Only few reports in literature document NMSs with video-electroencephalographic (EEG) and electromyographic coregistration. A multimodal evaluation is crucial to exclude common mimics and propose correct therapy. We describe a case of a 62-year-old man with drug-resistant focal epilepsy and NMSs, evaluated with video-EEG recording with polygraphy, magnetoencephalography (MEG), and brain magnetic resonance imaging (MRI). Video-EEG monitoring showed 182 focal NMSs, with preserved awareness and comprehension. The patient reported complex paresthesia of the left hand followed by left facial grimace, left arm flaccid paralysis, and bradycardia. EEG showed ictal discharges in the right frontocentral region associated with sudden electromyographical silence in left limb muscles consistent with loss of tonic contraction from distal to proximal muscles of the arm. MEG localized the epileptic zone in the right opercular region, consistent with MRI evidence of type II cortical dysplasia in the right inferior frontal gyrus. Multimodal evaluation is essential to document the temporal relationship between ictal discharges, clinical onset of limb paresis, and electrophysiologic evidence of loss of tonic muscular contraction. It allows definition of the specific cortical area involved in NMSs, offering new insight into physiological brain functioning.

Keywords: focal akinetic seizure; ictal bradycardia; ictal paralysis; negative motor area; negative motor seizures; video‐EEG polygraphy.

FIGURE 1

(A) Electroencephalograms with transversal montage recording from frontocentrotemporal regions (blue arrow shows seizure onset). Ictal activity is characterized by deflection, with low‐voltage fast activity superimposed mainly on right frontocentrotemporal regions. After later recruitment of the anterior and central vertex, fast activity is replaced by repetitive and irregular spike‐and‐waves on right frontocentral leads, with contralateral diffusion in the homologous derivations. Negative motor events first involve the left flexor carpi (1), then the left extensor carpi (2), and finally the bilateral proximal muscles with motor impersistence (deltoid; 3). The legs were recorded but not specifically tested. Electrocardiogram shows ictal bradycardia. Calibration: vertical line = 100 μV/cm, horizontal line = 1 s. (B) Brain magnetic resonance imaging shows lesion in the posterior portion of inferior frontal gyrus. The alteration appeared hyperintense on T2‐weighted/fluid‐attenuated inversion recovery sequences, associated with peculiar transmantle sign.

FIGURE 2

(A) In the upper right  panel, the position of the head and superconducting quantum interference devices (SQUIDs) for magnetoencephalography (MEG) is shown during the recording. The yellow area includes groups of SQUIDs whose traces are shown in panels B and F (each square is composed of two gradiometers and one magnetometer). (B, C) Butterflies of traces resulting from averaging of interictal epileptiform discharges (nine spikes) from the right frontotemporal gradiometers (B) and electroencephalographic (EEG; C) channels. (D, E) MEG source localization (standardized low‐resolution electromagnetic tomography, threshold = 86%) for the milliseconds with the maximal signal‐to‐noise ratio (corresponding to the red markers in B and C) is represented on cortex (D) and magnetic resonance imaging in the Montreal Neurological Institute space x = 176 (E). (F, G) The first part of seizure recorded by MEG (F; 1‐2‐3) and the corresponding source localizations of the ictal activity on cortex in different instants (G; 1‐2‐3), consistent with the presence of the dysplasia in right inferior frontal gyrus, albeit with slight differences (threshold = 76%).